The prior art includes motorized single wheel, self-balancing transportation devices. For example, FIGS. 1 and 3 of U.S. Pat. No. 8,616,313 (issued to Simeray for a Motorized Transport Vehicle for a Pedestrian) and FIGS. 1 and 6 of U.S. Pat. No. 8,807,250 (to Chen, the inventor herein, for a Powered Single-Wheeled Self-Balancing Vehicle for Standing User) illustrate such devices.
These figures represent at least two features of known single wheel transport devices. One is that the foot platforms are arranged so that a user, when riding, places his or her feet parallel to one another and aligned front to back, similar to how a person might stand while skiing. Another is that the motor and/or battery are placed within the wheel, for example, within the “envelope” of the wheel. One reason that the foot platforms are arrange in parallel is that the space within the wheel is occupied by the motor and/or battery and, therefore, there is insufficient space for the foot platform to extend into the wheel or wheel “envelope” (for purposes of this application, the wheel “envelope” refers to the space bounded by the wheel itself and the two parallel vertical side planes, one each on the exterior left and right sides of the wheel).
When standing, however, humans normally prefer to have the balls (i.e., front) of their feet turned slightly outward, often at 10-45 degrees (or other angle, depending on the person) from a line straight forward. Standing in this manner provides stability both front-to-back and side-to-side. A person standing with feet close together and parallel is less stable, side-to-side, than a person standing with the balls of their feet slightly splayed out.
Furthermore, when using a single wheel device, the center of weight, from a side to side perspective, is under the center of the wheel. If the feet are placed further out to the side and one foot is lifted, then the top of the wheel automatically tilts toward the non-lifted foot (with greater force the further out the foot is), thus small adjustments in weight (for example, mildly shifting one's weight) can cause significant instability in the device.
If the heel of a user or, in other words, the platform section on which the heel is placed, can be positioned closer to the center of gravity (side-to-side) of the wheel, then the device will be more stable.
In addition, the lower the platform, the more stable the device. Hence, it is desired to also have a user stand such that their heels are positioned relatively low to the ground. This also makes it easier and safer for a rider to get on or off the device.